Today, a variety of input-output devices are attached to electronic systems like a TV, a smartphone, an MP3 player, a PMP, a laptop computer, a PDA, etc. The various input-output devices are provided so as to allow a user to conveniently control the above systems. Since the smartphone, MP3 player, PMP, laptop computer, and PDA, etc., have a smaller size, there is a limit to attach the input-output devices. Therefore, a touch panel, a touch screen, a navigation pad, etc., are being increasingly attached as part of an effort to improve a user interface. Also, an integrated computer and tablet computer adopting the touch screen are distributed, so that there is a demand for various types of user interfaces.
Recently, a mouse and keyboard in a common personal computer is now being replaced with a touch screen capable of allowing the user to input data and to input commands even in a small space in various ways. Therefore, a variety of user interfaces on the touch screen are now being developed.
Though a conventional touch screen is used in various user interfaces without difficulty, the input through devices without the user interface has many limits, and thus, the user may feel inconvenient as much. For example, it is difficult to operate only by touching as accurately as the mouse and keyboard inputs, so that problems occur in games or web surfing. Specifically, when the user reads a book by using the conventional touch screen, the touch screen can be manipulated by two separate operations including zooming in and out on a portion that the user wants. Therefore, since the user who reads a book by using the conventional touch screen had to manipulate the two separate operations of zooming in and zooming out every time, there was an inconvenience.